Field of the Invention
The present invention relates to an infrared ray shielding film having excellent heat shieldability. More specifically, a second aspect of the present invention relates to a heat ray shielding material which has high visible light transmittance and a high mean solar reflectance, and is capable of reflecting infrared light over a wide band.
Background Art
In recent years, as one of energy saving measures for reducing carbon dioxide, heat ray shieldability-imparting materials have been developed for windows of vehicles and buildings.
As an infrared ray shielding filter, a filter using tabular Ag particles has been proposed (see Patent Literature 1). However, since the infrared ray shielding filter described in Patent Literature 1 is intended to be used in plasma display panels (PDP) and since such tabular Ag particles are not provided with configuration control, the filter mainly functions as a wavelength infrared ray light absorbent in an infrared ray region and does not function as a material that proactively reflects heat rays. Consequently, when the infrared ray shielding filter including such tabular Ag particles is used for shielding direct sunlight, the infrared ray absorbent filter itself would be warmed to increase the ambient temperature owing to the heat thereof and therefore its function as an infrared ray shielding material was insufficient.
Patent Literature 2 describes a wavelength-selective film using granular silver. In Patent Literature 2, an Ag layer in which granular silver particles are distributed is formed through Ag sputtering and heat treatment; and according to FIG. 3 in this reference, many granular silver particles have an atypical form.
On the other hand, Patent Literature 3 discloses a heat ray shielding material which has tabular metal particles having a hexagonal to circular form in a proportion of 60% by number or more and in which the main plane of the hexagonal to circular tabular metal particles is plane-oriented in a range of from 0° to ±30° on average relative to one surface of the metal particle-containing layer. Patent Literature 4 does not describe a preferred range of the thickness of the metal particle-containing layer, and in Examples therein, an aspect in which the metal particle-containing layer is from 0.1 μm to 0.5 μm, or that is, from 100 nm to 500 nm is disclosed.
Patent Literature 4 discloses a heat ray shielding material which contains hexagonal to hexagonal to circular tabular metal particles in a proportion of 60% by number or more, in which the hexagonal to circular tabular metal particles have two absorption peaks, and shield a relatively wide range of a wavelength region.
From the viewpoint of heat ray shieldability, a heat reflective type having no reradiation rather than a heat absorptive type one having indoor reradiation of absorbed light (in an amount of about ⅓ of the absorbed solar energy) is preferable, for which various proposals have been made. Since the infrared light in the sunlight is over a wide band, a heat ray shielding material that reflects infrared light over a wide band at 800 nm to 2,500 nm has been demanded from the viewpoint of solar reflectance.
Patent Literature 5 discloses a heat ray shielding material which has hexagonal to circular tabular metal particles in a proportion of 60% by number or more and a low coefficient of variation of the distribution of the distance between centers of silver particles.
Patent Literature 2 discloses a heat ray shielding material which has hexagonal to circular tabular metal particles in a proportion of 60% by number or more and in which the main plane of the hexagonal to circular tabular metal particles is plane-oriented in a range of from 0° to ±30° on average relative to one surface of the metal particle-containing layer.
Patent Literature 1 discloses an infrared ray shielding filter for a plasma display panel using tabular silver particles, which has excellent visible region transmittance and infrared ray shieldability.